check engine light came on and then off scanned 6 codes,10,121,176,511,542,543

[hottwheels04]

Like title states check engine light came on stayed on for a little then randomly went off on its own and did not come back on. I scanned it with the obd1 scanned I get 6 codes. 10,121,176,511,542,543.



1995 for mustang gt 5.0


I'm thinking fuel pump is going bad? 2 codes 542and 543 are to do with fuel pump. 1 code is rom failure. one code is to do with voltage to high, 1 is to do with 02 sensor.


Codes definition are as follows:


10= n0 defition for it?

121= closed throttle voltage higher or lower then expected

176= hego)ho2s) sensor fault/always lean

511=read only memory (rom test failure)

542= fuel pump secondary circuit fault


543= fuel pump secondary circuit fault


What do you guys think ? where to go from here

 

[07GtS197]

10 just means the ecu isnt in failure mode. Now with all the other codes Id put a fuel pressure tester on it to see where its at before doing anything else.

 

[hottwheels04]

10 just means the ecu isnt in failure mode. Now with all the other codes Id put a fuel pressure tester on it to see where its at before doing anything else.

so thats good thing ? I was thiking bad ecu, so 10 means the ecu is ok? and i read the 511 code is becaue its chipped / tuned. so the other codes are to do with 02 sensor or tps / voltage and 2 others are to do with fuel pump ect. I replaced the tps sensor and 02 sensors months ago. so I cant see it being that. so yeah I will see if i can do a fuel presssure tester. thanks for the help I will go from there.

 

[07GtS197]

so thats good thing ? I was thiking bad ecu, so 10 means the ecu is ok? and i read the 511 code is becaue its chipped / tuned. so the other codes are to do with 02 sensor or tps / voltage and 2 others are to do with fuel pump ect. I replaced the tps sensor and 02 sensors months ago. so I cant see it being that. so yeah I will see if i can do a fuel presssure tester. thanks for the help I will go from there.

Im not very familiar with obd1 since I sold my 85 vic a few years back so bear with me. The first code will either be a 10, 99 or 998. 10 is ecu pass self test and 99 and 998 are ecu is in failure mode.

Do you have a fuse box diagram? I dont see all these things failing at once. How much gas did you have when this happened? By the way adjusting the tps is a myth. Whatever the voltage is when the key is first turned is used by the ecu as the closed throttle value. If its too far above 1v though it will give you problems.

 

[hottwheels04]

Im not very familiar with obd1 since I sold my 85 vic a few years back so bear with me. The first code will either be a 10, 99 or 998. 10 is ecu pass self test and 99 and 998 are ecu is in failure mode.

Do you have a fuse box diagram? I dont see all these things failing at once. How much gas did you have when this happened? By the way adjusting the tps is a myth. Whatever the voltage is when the key is first turned is used by the ecu as the closed throttle value. If its too far above 1v though it will give you problems.

yeah I'm stumped I found a bad ground wire replaced it and car was running fine, I just filled up it had over half a tank of gas I got on it few times on the highway out of nowhere the check engine light came on stayed on and then went off so i went home and scanned it these codes came up but no check engine light was on when i turned the car back on ? lol

 

[hottwheels04]

just started it no check engine light. its showing only 2 codes now 121 , 543 121 is

121= closed throttle voltage higher or lower then expected

543= fuel pump secondary circuit fault


no check engine light but when i scan it those 2 codes still come up when i test it.

 

[07GtS197]

Im leaning towards a failing fuel pump but you need to get a fuel pressure tester on it before moving on. Most likely the codes will clear after it starts running again. Also you know you have to get it up to normal operating temp before checking codes.

 

[hottwheels04]

Im leaning towards a failing fuel pump but you need to get a fuel pressure tester on it before moving on. Most likely the codes will clear after it starts running again. Also you know you have to get it up to normal operating temp before checking codes.

I was thinking fuel pump to, but now im leaning towards o2 sensor drivers side. I had a guy test fuel pressure with a tester its fine. so doesnt look like the pump. but i noticed when i let the car sit and test it not operating temp like you said its the votage 121 and 543 pump code. but once i drive it and warms up then scan it it throws code # 176= hego)ho2s) sensor fault/always lean


Looks like driver side 02 sensor is going bad? once it warms up it throws the ecu and pump off its making it lean out to much which sounds lke ti throws the pump code along with it?

 

[07GtS197]

I would check the wiring first then replace the o2 sensor. I dont like to suggest throwing parts at a problem but thats what this looks to be. You can also look and listen for exhaust leaks near the o2 sensor.

 

[hottwheels04]

I would check the wiring first then replace the o2 sensor. I dont like to suggest throwing parts at a problem but thats what this looks to be. You can also look and listen for exhaust leaks near the o2 sensor.

Yeah i replaced the bad ground wire, put in new 02 sensors and put in a new tps sensor. will drive it for 100 miles and hopefully be good to go knock on wood.

 

[Silver95bird]

Just for shytes and giggles, I'd also be monitoring the voltages, connections, and grounds anywhere near the problem spots. Wouldn't hurt to check battery connections as well. You found one, there could always be more. Goofy stuff like an intermittent alternator/regulator can also cause erratic signals too.